The compound expressed by the general formula (3) is used as a stabilizer and a fire retardant for organic low molecular weight and high molecular weight compounds, and also, is used as a quality-improving material and a yield-improving material in production of these compounds. This compound is an important material that is used as a raw material in production of many stabilizers, fire retardants and retardative organic high molecular weight compounds.
The compound expressed by the general formula (2) is important as a raw material for production of the compound expressed by the general formula (3), and also, is important as a raw material in production of stabilizers and fire retardants for organic low molecular weight and high molecular weight compounds. Both the compounds are expected furthermore to extend their use in the future.
For producing the compounds expressed by the general formula (2) and general formula (3), there is known a conventional process which comprises heat-condensing a o-phenyl phenol compound expressed by the general formula (4) ##STR3## wherein R.sub.1, R.sub.2 and R.sub.3 are the same as defined in the general formula (3) and a phosphorus trihalide expressed by the general formula (5) EQU PX.sub.3 (5)
wherein X is chlorine or bromine in the presence of Friedel Crafts catalyst to produce a compound expressed by the general formula (1) ##STR4## wherein R.sub.1, R.sub.2, R.sub.3 and X are the same as defined in the general formula (4) and (5), pouring the resulting compound into the excess amount of water, followed by and hydrolysing under heating and precipitating under cooling, or pouring the resulting compound into an aqueous solution of an alkali metal hydroxide, hydrolysing under heating, acid-precipitating after cooling to produce a compound expressed by the general formula (2), followed by cyclising-dehydrating under heating to produce a compound expressed by the general formula (3) (see, for example, Japanese patent publications Nos. Sho 45397/1974 and Sho 17979/1975).
Also, there is proposed a process of producing a compound expressed by the general formula (3) by hydrolysing a compound expressed by the general formula (1) with equivalent mol of water in the presence of organic solvent (see Japanese Patent Laid Open No. Hei 145185/1995).
However, in case that the compounds expressed by the general formula (2) and the general formula (3) obtained by such processes are used as the stabilizers and fire retardants for organic low molecular weight and high molecular weight compounds, particularly in case of using as electronic materials and synthetic fibers, further in case of using as a semiconducter-sealing and a raw material of high molecular weight compounds for producing synthetic fibers, the compounds of high purity and high quality are required, so that the products obtained by the conventional processes are difficult to satisfy these requirements.
Therefore, there were attempted purification methods such as vacuum-distillation purification before hydrolysis or recrystalization purification by an inert organic solvent in case of a compound expressed by the general formula (1), or acid-precipitation purification after active carbon treatment of aqueous solution of an alkali metal hydroxide, or recrystalization by the mixed solution of alcohol and water in case of a compound expressed by the general formula (3). However, since either purification has a problem in the yield and/or is insufficient in removal of inorganic and/or organic impurities, the aim has not been attained so far.
An object of the present invention is to provide a product of high purity and high quality without using an alkali or a particular chemical, a complicated operation such as vacuum distillation or an equipment made of specific materials.